There has lately been known an image reading apparatus that reads digitally an image recorded on a photographic film by the use of a reading sensor such as CCD (Charge Coupled Device). On the image reading apparatus of this kind, light is projected on a photographic film on which an image is recorded, and its transmitted light is read photoelectrically by a CCD line sensor, and thereby, the image thus read is subjected to digital conversion to obtain digital image data. In general, a halogen lamp is used as a light source by which a photographic film is irradiated with light.
Further, a photographic image processing system that converts an image obtained through photographing by a camera into digital image data is proposed and is put to practical use. In this system, there is used an image processing apparatus in which a document such as a negative film obtained through photographing by a camera is read by a film scanner (image reading section), and is converted into digital image data to be recorded.
On the film scanner (image reading section) constituting the image processing apparatus, there is provided a light-emitting mechanism that projects prescribed light on a document. The light that is emitted from this light-emitting mechanism and is transmitted through the document or reflected on the document is received by a light-receiving means such as CCD, and is read as image information.
However, in the image reading apparatus that employs a halogen lamp mentioned above as a light source, there has been a problem that colors of images read are ill balanced, because a color balance of a light source cannot be controlled. For example, as shown in FIG. 7, a color balance of images read is lost because an amount of transmitted light on a negative film base (non-image area) differs depending on wavelengths, namely, on colors (R, G and B).
On the other hand, there is proposed a light-emitting mechanism equipped with a prescribed light source and a light-converging means for converging light emitted from the light source. In the past, a halogen lamp was used as a light source. However, it was impossible to irradiate a document with light that is well balanced from the short wavelength side to the long wavelength side, because spectral component of the light that is emitted from the halogen lamp was biased to the long wavelength side. Therefore, output of accurate image information was disturbed.
Further, a decline and unevenness of an amount of light emitted from the light source were unavoidable under the condition of only light-converging means equipped on the conventional light-emitting mechanism, resulting in occasional deterioration of image quality of the image read.